Q4 2020: Record wind output and curtailment

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Dr Iain Staffell, Professor Richard Green, Professor Tim Green, Professor Rob Gross and Dr Malte Jansen -Imperial College London

Britain’s wind farms hit an all-time high in 2020.  

They supplied more than a quarter of the country’s electricity demand over the year, but that also meant more of their potential output had to be discarded due to network congestion. Curtailment almost doubled from 2019, at a cost of over a quarter of a billion pounds.

Over the year as a whole, wind farms supplied 69 TWh of electricity, but this could have been much more.  6% of Britain’s wind output had to be curtailed – or wasted – because it couldn’t be transported to consumers on the electricity network.  3.8 TWh of electricity was lost to curtailment over the year, enough to power every home in Wales.[1]  

Annual curtailment of wind energy in Britain over the last decade [left] and the cost of this curtailment against total output [right]

Between 2015 and 2019, curtailment costs rose in line with wind output from £90 to £145 million per year. This cost doubled in 2020 though, as National Grid ESO faced a bill of £282 million – around £10 per household. Put another way, curtailment costs added £4 to each MWh of wind energy generated. While this pushes up the whole-system cost of generation, wind is still likely to give lower bills than a system dominated by fossil fuels and nuclear, as its construction costs have come down so far.

Much of Britain’s onshore wind is in the central belt of Scotland, and there is often congestion on the lines which carry this down to other demand centres in England and Wales.  We last reported on constraints in 2018 when a new transmission line (the Western HVDC link) came online, adding more capacity between Scotland and the rest of Britain.  That link was offline for much of January and February, giving rise to high curtailment (more than 6% of the wind generated) in those months.  Ofgem is now investigating the link over its performance.

Wind curtailment was also high during the summer months as demand was depressed during lockdown. Rates went back down during Quarter 3 as lockdown restrictions eased and demand rose, but then in November curtailment rose to a new peak with more than 11% of wind energy lost.  National Grid’s service to deliver more operational flexibility came to an end, and the Western Link suffered more outages.  

Ultimately, some level of curtailment should be accepted as part of the most cost-effective way to deal with wind over-production. The cost of new transmission lines and storage is still relatively high, so in the short-term it is cheaper to continue paying wind farms to shut down than to invest in more technical fix. Eliminating all curtailment would involve massive infrastructure investments, but it is natural to want to make the most of the renewable resources we have. New innovations such as smart-charging electric vehicles or flexible production of hydrogen could eventually help to ease the situation.

[1] This curtailed energy could have powered around 1.25 million homes (assuming the UK average of 3,000 kWh per year), or around 3 million people.  The population of Wales is estimated at around 3.2 million. 

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